powerpc/mm: Add Strong Access Ordering support

Allow an application to enable Strong Access Ordering on specific pages of
memory on Power 7 hardware. Currently, power has a weaker memory model than
x86. Implementing a stronger memory model allows an emulator to more
efficiently translate x86 code into power code, resulting in faster code
execution.

On Power 7 hardware, storing 0b1110 in the WIMG bits of the hpte enables
strong access ordering mode for the memory page.  This patchset allows a
user to specify which pages are thus enabled by passing a new protection
bit through mmap() and mprotect().  I have defined PROT_SAO to be 0x10.

Signed-off-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/syscalls.c b/arch/powerpc/kernel/syscalls.c
index 4fe69ca24481..c04832c4a02e 100644
--- a/arch/powerpc/kernel/syscalls.c
+++ b/arch/powerpc/kernel/syscalls.c
@@ -143,6 +143,9 @@ static inline unsigned long do_mmap2(unsigned long addr, size_t len,
         struct file * file = NULL;
         unsigned long ret = -EINVAL;
 
+        if (!arch_validate_prot(prot))
+                goto out;
+
         if (shift) {
                 if (off & ((1 << shift) - 1))
                         goto out;